STM reveals molecular first
http://physicsweb.org/articles/news/9/10/11/1
20 October 2005
Physicists have observed the Jahn-Teller effect in a molecule for the
first time. The effect was seen in carbon-60 molecules doped with
potassium. The results could shed more light on the fundamental
properties of molecular nanostructures (Science 310 468).
"The Jahn-Teller effect has long been known to play an important role
in the relationship between the structure of molecules and their energy
levels, but this is the first time anyone has directly imaged it at the
single-molecule level," says Mike Crommie of the University of
California at Berkeley and the Lawrence Berkeley Laboratory, leader of
the team that saw the effect.
The Jahn-Teller effect occurs in systems that can exist in two or more
distinct states that have the same energy. Because such a "degenerate"
system is unstable, a molecule will distort itself to split the energy
levels. Pure carbon-60 is an insulator because its highest occupied
molecular orbital (HOMO) is full of electrons, while the lowest
unoccupied molecular orbital (LUMO) is empty. The HOMO state is 5-fold
degenerate, while the higher-energy LUMO state is 3-fold degenerate.
See: http://physicsweb.org/articles/news/9/10/11/1
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